Pneumatic air suspension systems commonly consist of an air tank that supplies air to air springs installed at the axles in between the vehicle frame or body. The air tank is connected to the air springs through a series of hoses and connectors that transfer air from the tank to the air springs. In some cases, check valves and regulators are incorporated in line with air hoses, in order to provide the necessary protection to prevent over-inflating the air springs or depleting the air tank in case of air spring failure. The pneumatic suspension commonly incorporates a load-leveling valve that can adjust the pressure in the air spring based on the wheel load or the vehicle load.
Most common air suspensions in vehicles including, but not limited to, heavy trucks use a mechanical load leveling valve that adjusts the air pressure within the air suspension in response to the load placed on the suspension. When the vehicle is loaded, the air pressure is increased for higher suspension stiffness and better support of the added weight (load) placed on top of the suspension. Conversely, when load is removed, air pressure is decreased to provide a softer suspension and prevent the frame from jacking up. The end result is a truck that rides “level,” meaning it rides at the same ride height independent of its loading condition.
The load leveling is accomplished through the aforementioned mechanical leveling valve, commonly referred to as a “load leveling valve,” or a “ride-height control valve.” Some truck configurations employ two leveling valves, one on each side, for the main purpose of better responding to any uneven roads or forces at the suspension on each side, independently. In such systems, the leveling valves attempt to keep each side level, therefore achieving a side-to-side leveled truck. In either a single valve suspension system or a double valve suspension system, leveling valves of the prior art were designed only to supply or exhaust air in an alternating sequence. As a result, the air springs attached to a conventional leveling valve may all uniformly receive air from the leveling valve or may all uniformly discharge air to the leveling valve. In other words, conventional leveling valves are not capable of simultaneously supplying air to a first set of attached air springs while discharging air from a second set of attached air springs.
FIG. 1 illustrates one conventional suspension system of the prior art comprising a single leveling valve connected to a plurality of springs, in which each spring is formed by an air bag. Because conventional leveling valves may only supply or remove air in an alternating sequence, all the air bags in the suspension system of FIG. 1 are either supplied air from the single leveling valve or exhausted air from the single leveling valve. Consequently, the suspension system of FIG. 1 is not able to alter the height of one side of the vehicle without making the same change to the other side of the vehicle, thereby lacking the capability to account for unbalanced loading of the vehicle and/or weight shifts. Thus, for suspension systems with one leveling valve, once the truck body is leveled to the set height, the valve remains predominantly closed, in that the level valve does not remove or add any air to the suspension air springs even in the event of a weight shift.
One attempt in the prior art to account for unbalanced loading and weight shifting of a vehicle was to provide a suspension system utilizing two load level valves with one valve placed on each side of the vehicle, as shown in FIG. 2. For suspensions with two load leveling valves, the air in each side can be adjusted such that the truck remains statically, and in some cases dynamically, leveled. For instance, when the truck is unleveled side-to-side, one side is raised while the other side is lowered. In such a case the leveling valve on the lower side adds air to the suspension, whereas the valve on the other side does the opposite by removing air from the suspension to lower the raised side. Thereby, the leveling valves on the two sides perform diametrically opposite actions: one releases air while the other one adds more air. One leveling valve increases the suspension stiffness on one side while the other reduces it on the opposite side. However, incorporating a second leveling valve into the suspension system requires more air hoses and couplings, thereby adding cost to the suspension system and increasing the likelihood of maintenance. Moreover, irrespective of whether a suspension system uses one or two conventional valves, the design of these conventional valves results in application of the same or similar action on the air springs, i.e., either adding or retracting air from the air springs.
Furthermore, conventional valves are designed to reduce the possibility of overcompensating or undercompensating air pressure within the air springs by hindering the air flow rate of the valve as the valve is initially actuated. Accordingly, more time is needed after actuating the leveling valve to set the air springs to a desired air pressure. Although hindering air flow at the initial actuation stage of the valve may prevent the air springs from losing or receiving too much air, conventional valves are slow to respond to dynamic, side-to-side or front-to-back weight shifts that often take place as the vehicle is moving. Such weight shifts occur as a result of the vehicle traveling on a curved roadway, or during acceleration and deceleration. Thus, conventional valves tend to respond too late to an impulsive weight shift of a moving vehicle, ultimately increasing the likelihood of the vehicle overturning at a sudden change of movement, such as a sharp turn. Such rollovers are often disastrous.
Accordingly, there is need for a dual action leveling valve that can simultaneously supply air to a first set of springs and exhaust air from a second set of springs so that a one leveling valve suspension system can account for unbalanced loading of a vehicle. Furthermore, there is need for a leveling valve that responds quickly to a dynamic weight shift in a moving vehicle to reduce the risk of the vehicle overturning at a sudden change of movement, such as a sharp turn.